Email has become an increasing popular way to communicate. A number of email systems are commercially available, including Microsoft Exchange, IBM Lotus Notes, Sendmail, Postfix and others. The format of email messages in general usage is that defined by the Multipurpose Internet Mail Extensions (MIME) standard. MIME-compliant email messages consist of two major sections: the header and the body. The header includes information regarding the sender, the receiver, a subject line or summary, the time and date that the message was originally sent and other information about the email. The body is the message itself, and may include or be composed of text or files of various types.
Each header field typically has a name and a value. For example, the value for the receiver or “To” field in the header typically is the person or entity to whom the email is addressed. The person listed in the “To” field is not necessarily related to the address or addresses to which the message is delivered. The actual delivery list is supplied in the envelope, not extracted from the header content. The “To” field is similar to the greeting at the top of a conventional letter which is delivered according to the address on the outer envelope. For example, the salutation on the letter can be “Resident” while the envelope address can read “John Doe”. Similarly, the sender or “From” field does not have to be the real sender of the email message. In fact, it is very easy to falsify the “From” field so that a message seems to be from one entity when it actually originated from someone else. Other information in the header is also susceptible to misrepresentation.
It would be helpful if there were a way to pass information securely between distributed email servers using metadata in email in a way that limits or eliminates the potential for misrepresentation by an untrusted party in such a way as to eliminate duplicative processing while allowing for separation of function. To date no such means are known.